Systems and methods for noise suppression are necessary components and/or applications in many communication systems including those using radio frequency (RF) technologies and/or optical technologies.
In particular, a simple approach for noise suppression in a communication system is disclosed in U.S. Pat. No. 5,533,133, which is incorporated by reference herein in its entirety. This approach proposed to suppress the noise during pauses and silent periods in a conversation. The approach does not allow for noise subtraction from a received signal and it provides just perceptibly improved quality of communication.
An approach for actual noise suppression of a communication signal in a communication system was proposed in U.S. Pat. No. 6,865,276, which is incorporated by reference herein in its entirety. This method for noise suppression suppresses a disturbance signal using a priori information about a fundamental frequency of the disturbance signal to generate an estimate of this disturbance signal. This estimated disturbance signal is subtracted from the communication signal. The basic drawback of this method is that it is necessary to have a priori information about the noise to suppress the noise.
Another approach for noise suppression of a communication signal in a communication system was proposed in U.S. Patent Publication No. 2004/0052533, which is incorporated by reference herein in its entirety. Specifically, referring now to FIG. 1, the approach proposed using a system for noise suppression in optical communication which includes two transmitters operating at two different wavelength. One of the transmitters (Data A in FIG. 1) is used to send an information signal and the other one (1 in FIG. 1) is used to send a stable reference signal. For noise suppression, the approach proposed to extract the noise from the reference signal and than subtract it from the information signal supposing that both signals acquired similar noise during propagation. The basic disadvantage of this approach is that in reality, the spectral density of noise depends on wavelength; therefore, the subtraction of noise measured at one wavelength from a received signal measured at another wavelength can give good result only for some special communication systems. However, in a typical communication system, for example in a broadband communication signal application (using short laser pulses and/or conventional multichannel WDM/DWDM technologies), this approach does not provide for good noise suppression because of the spectral dependences of noise.
It is therefore desirable to provide a system and method for suppression of noise in communication system that overcomes the above-described shortcomings while retaining their advantages. In particular, it would be desirable to provide a system and method that can realize spectral suppression of noise in communication systems.